A U.S. helicopter crashed in Iraq on Monday morning, killing one and injuring at least three others, American officials said in a statement, marking the second fatal crash so far this year.

Joint Operation Inherent Resolve, the U.S.-led mission to destroy the Islamic State in Iraq and Syria, said the incident was not the result of enemy fire.

“The aircraft was conducting a partnered counterterrorism mission in support of Operation Inherent Resolve,” military officials said in a statement. “All personnel were recovered by coalition forces immediately following the incident, and three were evacuated for further treatment. There are no indications the crash was caused by hostile fire. The incident is under investigation.”

The military did not release any further details. Newsweek reported Monday that the helicopter was returning from a small-scale raid and likely suffered some sort of mechanical malfunction.

Monday’s incident is the second fatal helicopter crash so far this year. In March, a U.S. helicopter went down in Iraq’s Anbar Province, killing seven service members.